Some vehicle engines include a cylinder block having a cylinder head coupled to an upper part thereof and a lower crankcase coupled to a lower part thereof. The cylinder block and lower crankcase function as a crank supporter. That is, a bearing holder in the cylinder block and a bearing holder in the lower crankcase respectively maintain a bearing in the cylinder block and a bearing in the lower crankcase for supporting the crankshaft.
In addition, the crankshaft is typically cast of iron. For weight reduction, the cylinder block and the lower crankcase are cast of aluminum alloy. When forming the cylinder block and the lower crankcase of aluminum alloy, materials having lower thermal expansion than that of aluminum alloy are cast (embedded) therein to reduce thermal expansion of the bearing holders. Fiber-reinforced metal (FRM) is employed as one of the methods for casting. More particularly, the fiber-reinforced material is fired and shaped into a certain form to produce a preform body (a core). By penetrating aluminum alloy into the preform body during casting of the lower crankcase, the preform body of fiber reinforced material is formed into the crankcase to reduce thermal expansion of the bearing holder. This reduces oil clearances between the crankshaft and the bearing holder, and reduces vibration or noise.
Referring to FIG. 17, an engine 202 mounted on a vehicle (not shown) includes a cylinder head (not shown) on top of a cylinder block 204, a lower crankcase 206 at the bottom of the cylinder block 204, and an oil pan 208 at the bottom of the lower crankcase 206. The cylinder block 204 and lower crankcase 206 are formed by e.g., die casting, with the casting material being aluminum alloy.
A semicircular bearing holder 210 in the cylinder block 204 and a semicircular bearing holder 212 in the lower crankcase 206 respectively sustain bearings 214, 216 to support a crankshaft 218 therebetween. The crankshaft 218 is made of iron.
The cylinder block 204 includes cylinder bores (not shown) for cylinders formed longitudinally in series by cores (not shown) during casting. Blowby passages 222-1, 222-2 are formed adjacent outer walls 220-1, 220-2 in the cylinder block 204, which passages extend upwardly and open at top ends. In the lower crankcase 206, upwardly extending blowby passages 226-1, 226-2 are formed by cores (not shown) during casting and are adapted to communicate with the blowby passages 222-1, 222-2, and are positioned adjacent outer walls 224-1, 224-2. The blowby passages 222, 226 also serve as an oil drop to permit downwardly flow of oil from above.
Threaded coupling bolt screw holes 228-1, 228-2 are defined in the bearing holder 210 of the cylinder block 204 and open at the bottom wall 204B thereof. A main oil gallery 230 is formed toward an upper part of the blowby passage 222-2. A journal oil passage (i.e. oil supply hole for the crank journal) 232 extends upwardly from an inner circumference of the bearing holder 210 to communicate with the gallery 230.
First and second case bolt holes 234-1, 234-2 are defined in the lower crankcase 206 to communicate with the coupling bolt screw holes 228-1, 228-2 in the cylinder block 204. More than one oil pan mounting screw holes 236 are defined in an outer flange of the crankcase at a bottom 206B thereof. On an outer surface 212F of the bearing holder 212 in the lower crankcase, a protruding portion 238 is formed and extends to the bottom surface 206B. The protruding portion 238 has a parts mounting bolt screw hole 240 for mounting parts, and one end 240E of the hole 240 opens downwardly.
The cylinder block 204 has the cylinder head (not shown) threadedly fixed thereto from above by mounting bolts (not shown). In the lower part of the cylinder block 204, the lower crankcase 206 is fixed to the cylinder block 204 by inserting first and second case mounting bolts 242-1, 242-2 from below into coupling bolt screw holes 228-1, 228-2 through the first and second case bolt holes 234-1, 234-2. A parts mounting member 246 is attached to the crankcase 206 by a parts mounting bolt 244 that is threadedly attached to the screw hole 240. An oil pan 208 is attached to the lower crankcase 206 by oil pan mounting screws (not shown) that are inserted into the mounting screw holes 236.
The bearing holder 212 in the lower crankcase 206 includes a formed body 248 with a fiber-reinforced metal (FRM) portion. The body 248 is formed by penetrating aluminum alloy into a preform member (a core material) 250 when casting the lower crankcase 206. The preform member 250 is shaped into a form adapted to a shape of the bearing holder 212 in the crankcase by firing the reinforced fiber material, and the formed body 248 having the FRM portion is produced by penetrating aluminum alloy into the preform 250 when casting the lower crankcase 206.
As shown in FIGS. 18 and 19, the preform member 250 includes first and second bolt insert holes 254-1, 254-2, in first and second cylindrical bolt support sections 252-1, 252-2, that vertically penetrate through upper and lower surfaces 250U, 250B and are shaped by a mold (not shown). Also, a recessed section 256 is preformed adjacent the bottom of the preform member 250. The recessed section 256 includes therein a cylindrical concave-shaped hole 258 that has a bore diameter Ø and a predetermined depth D measured from the bottom surface 250B so as to accommodate the bottom 240B of the screw hole 240.
Referring to FIG. 20, the lower crankcase 206 is formed when aluminum alloy is poured as molten metal (matrix) into a casting mold 260 to cast the preform member 250 inside. The mold 260 includes upper and lower mold parts 260-1, 260-2. The upper and lower mold parts 260-1, 260-2 have first upper and lower pins (not shown) corresponding to the first case bolt hole 234-1, and second upper and lower pins (not shown) corresponding to the second case bolt hole 234-2.
In casting, as shown in FIG. 20, the lower crankcase 206 is turned upside down and is positioned in a space 262 of the lower mold part 260-1. The upper surface 250U of the preform member 250 is aligned with a plane at a certain distance above the bottom of the space 262. The bottom 250B of the preform member 250 is aligned with a plane at a certain distance below a bottom of the upper mold part 260-2. The sides 250C are aligned with planes at a certain distance from the sides of the space 262. A reentrant 264 is formed in the upper mold 260-2 at a position aligned with the hole 258 to define the protruding portion 238.
In casting the lower crankcase 206, the molten metal is poured through a left inlet 266 at an upper part of the lower mold part 260-1. The molten metal passes through the lower mold part 260-1 and around the preform member 250 and to a right outlet 268 at the upper part of the lower mold part 260-1. The molten metal of aluminum alloy penetrates into the preform member 250 to form the FRM portion of the formed body 248. After casting, the parts mounting bolt screw hole 240 is processed for threading so as to project into the hole 258 defined in the recessed portion 256.
Such crankshaft supporter is disclosed in e.g., JP Laid-Open Nos. 2002-61538, 2000-337348, and 2001-71117 Official Gazettes. According to the crankshaft supporter disclosed in JP Laid-Open No. 2002-61538, and corresponding U.S. Pat. No. 6,543,334, both owned by the Assignee hereof, a lower crankcase includes an aluminum alloy layer in sliding portions of a bearing supporter, and a composite material around the aluminum alloy layer, which composite material has a lower coefficient of thermal expansion than that of the layer. According to the crankshaft supporter disclosed in JP Laid-Open No. 2000-337348, a bearing supporter in a lower crankcase is formed of a porous material, and a material around the bearing supporter is flowed into pores of the bearing supporter. According to the disclosure in JP Laid-Open No. 2001-71117, a particular section corresponding to a side of a preform member to which molten metal is poured has a rigidity greater than that of other parts.
As shown in FIG. 20, in the conventional crankshaft supporter, when the bearing holder to support the bearing for the crankshaft is molded in aluminum alloy, that is, when the bearing holder of the lower crankcase 206 is molded in aluminum alloy, the preform member 250 including reinforced fiber of lower coefficient of heat expansion is cast (embedded) inside of the bearing holder 212 so as to prevent vibration or noise resulting from clearance of the bearing 216 in the lower crankcase by heat expansion. In addition, when the hole 240 having the opened lower end 240E is to be formed in the outer surface 212F of the bearing holder 212 so as to attach the parts mounting member 246, since the preform member 250 is hard (rigid) and difficult to machine, the hole 258 is pre-formed in the preform member 250 so that the aluminum alloy layer is deposited inside in order to improve cutting or machining of the screw hole 240.
However, the hole 258 is formed in a cylindrical shape with a bottom portion corresponding to the bottom portion 240B of the screw hole 240 as shown in FIG. 17. Due to this shape, the molten metal does not properly flow to the bottom 258B of the hole 258 during casting, thereby producing undesirable blowholes (cavities) P as shown in FIG. 21.
To obviate or minimize the above problem, the present invention provides an improved crankshaft supporter. A bearing holder molded in aluminum alloy supports a bearing that supports a crankshaft. A preform member is cast inside of the aluminum alloy. A screw hole having one opened end is formed in an outer surface of the bearing holder. A concave recess section is formed in the preform member to accommodate a bottom of the screw hole. An introduction means is provided in the recess section to introduce molten metal therein during casting.
According to the present invention, the screw hole having one opened end is defined in the outer surface of the bearing holder, and the concave recess section in the preform member is formed to accommodate the bottom of the screw hole, and the introduction means is provided in the recess section to introduce molten metal therein during casting. As a result, the molten metal is introduced to the bottom of the recess section to effectively prevent blowholes.